Yankee dryer head and brace

ABSTRACT

A rotary pressure vessel of the type used in various settings as dryers for slurries, sludges, webs, etc., including a shell with a pair of two-piece end walls or heads at each end of said shell. The inner portion of each head, i.e., adjacent to a journal, is formed integral with the journal. The outer portion of each head serves to connect the inner head portion to the dryer shell. The radial dimensions of the inner and outer portions are adjusted so as to provide a minimum level of stress at the joint between the inner and outer head portions. The rotary pressure vessel also includes a brace, in the form of a cylindrical shell, arranged between the pair of outer head portions. The size of the brace is selected so that it may be fabricated from standard flanges and pipe or rolled plate and at the same time relieves the shell of projected end loads.

United States Patent [191 Lande [451 Oct. 14, 1975 YANKEE DRYER HEAD AND BRACE Stanley H. Lande, Newport News, Va.

[22] Filed: Apr. 23, 1974 [21] Appl. No.: 463,239

[75] Inventor:

[52] US. Cl. 34/110; 34/124; 165/90 [51] Int. Cl. F268 ll/02 [58] Field of Search 34/108, 109, 110, 111,

Primary Examiner-Kenneth W. Sprague Assistant ExaminerJames C. Yeung Attorney, Agent, or Firm-Pollock, Philpitt & VandeSande ABSTRACT A rotary pressure vessel of the type used in various settings as dryers for slurries, sludges, webs, etc., including a shell with a pair of two-piece end walls or heads at each end of said shell. The inner portion of each head, i.e., adjacent to a journal, is formed integral with the journal. The outer portion of each head serves to connect the inner head portion to the dryer shell. The radial dimensions of the inner and outer portions are adjusted so as to provide a minimum level of stress at the joint between the inner and outer head portions. The rotary pressure vessel also includes a brace, in the form of a cylindrical shell, arranged between the pair of outer head portions. The size of the brace is selected so that it may be fabricated from standard flanges and pipe or rolled plate and at the same time relieves the shell of projected end loads.

8 Claims, 5 Drawing Figures US. Patent Oct. 14, 1975 Sheet 1 of2 3,911,595

FIG. I.

(Prior Art) U.S. Patent Oct. 14, 1975 Sheet 2 of2 3,911,595

Iii-L (Prior Art) FIG. 5.

YANKEE DRYER HEAD AND BRACE FIELD OF THE INVENTION This invention relates to rotary pressure vessels useful as dryers, and more specifically to Yankee dryers so called because they are used with Yankee paper making machines. More particularly, the present'invention is concerned with a novel head and brace for the Yankee dryer which provides the necessary supporting functions and at the same time is simpler andeasier to manufacture and thus significantly reduces the costs involved as compared with the prior art.

BACKGROUND OF THE INVENTION Rotary pressure vessels have been used to perform a drying function in a variety of settings for a number of years. Commonly, the object to be dried, which may be a slurry, sludge or web, comes into contact with the shell of the rotary pressure vessel. A heat transfer medium, usually steam, is introduced into the interior of the rotary pressure vessel and provides heat to the object to be dried. This heat is transferred from the heat transfer medium through the shell of the rotary pressure vessel. One common application of such rotary pressure vessels is in the paper making industry. When such rotary pressure vessels are combined with Yankee paper making equipment they are generally termed Yankee dryers. The dryer per se comprises a shell, a pair of end walls commonly known as heads, and shaft and journal upon which the shell and heads are mounted for rotation. Suitable apparatus is provided to introduce the heat transfer medium, usually steam, to the interior of the Yankee dryer and to remove the spent heat transfer medium. It has also been found useful, in the manufacture of Yankee dryers to provide a brace which is normally coupled between the heads as an additional structural element.

It should be readily apparent to those skilled in the art, that the dryers are subject to widely varying temperature and pressure conditions. Thus, during idle periods the dryer will be subject to ambient pressure and temperature. Under normal operation, the internal steam pressure can rise to 125 p.s.i.g. or more at temperatures in excess of 300 F. These widely varying temperature and pressure conditions obviously induce large thermal stresses in the dryer. In addition, the dryers are physically massive structures which may be to feet in length with diameters ranging to 18 feet and more. The shell commonly is cast iron about 2 inches thick. Since the heads alone support the shell and, in normal operation the shell is rotating, large mechanical stresses are experienced by the heads in addition to the substantial thermal stresses.

The quest for ever greater efficiencies is evidenced by a trend toward physically larger dryers, operating at higher temper'atures, pressures and velocities. These factors tend to require more massive structures to withstand the increased mechanical and thermal stresses. At the same time, however, the same goal of efficiency results in a desire to simplify and reduce the cost of manufacture of the dryers. A corollary of the foregoing is a desire to reduce the size of the dryer components, for a number of reasons. In the first place, reducing the size of the components results in a simpler manufacturing operation as smaller work pieces can be utilized. Secondly, as the dryer components are reduced in size, they approach the size of standard components. Obviously, the use of standard components is a desirable result since it reduces the special machining and fabrication steps that would otherwise have to be involved in the manufacture. It should be apparent that the push for greater efficiencies raises these, and other, conflicting trends.

PRIOR ART The prior art has attempted to resolve the problems introduced by the conflicting goals outlined above in a variety of fashions. One class of prior art solution is typified by Daane, U.S. Pat. No. 3,675,337 and Donaldson, U.S. Pat. No. 2,979,830. In both these structures, the heads are unitary and furthermore are integral with the journals. A second variety of solutions is typified by Malmstrom, U.S. Pat. No. 3,099,543; Hornbostel, U.S. Pat. No. 2,651,114 and Orstertag, U.S. Pat. No. 2,628,433. In this arrangement the heads are separate from the journals and they are attached thereto by a means of a flange which is integral with the journal. A variant of the latter type of prior art structure includes a similar journal with a flange for attachment to the head and a head structure connected between the journal flange and the shell. However, in this variety, the flange is extended, in a generally perpendicular relationship to the shaft, to such an extent that it forms part of the head. Thus, the head can be thought of as comprising an inner and outer portion, the inner portion being integral with the journal and the outer portion in the shape of an annulus. Furthermore, a brace is also included, which may take the form of a right cylinder, which may be thought of as an inner shell. This brace has been connected between parallel heads, and furthermore has been connected between the parallel inner head portions. An example of this is Ostertag, U.S. Pat. No. 3,060,592. Ostertag, U.S. Pat. No. 2,628,433, might be thought of as falling in this class as well.

The first class of prior art solutions itself presents a number of problems. The head integral with the journal requires machining on a work piece of substantial proportions. The radius of the head may be anywhere from 6 to 10 feet and thus the work piece may be as large as 20 feet in diameter. Accurately machining the journal portion of such a work piece is a time consuming and expensive operation. Furthermore, the size of the work piece limits the tools which one can use in machining it.

The second class of prior art dryer heads, including the variations thereof, pose a different, but no less serious problem. In that arrangement, it will be recalled, the head is attached to the journal by a means of a flange. Referring to FIG. 2, which shows such a head 23 attached to a journal 26 by a means of a flange 33; the particular serious difficulty encountered in this arrangement is that the attachment 37 is located at a particularly disadvantageous point. The flange of the journal is a location of maximum bending moment in the head. Therefore, a joint at this location must be capable of withstanding this bending moment. This requires an excessively large joint, or correspondingly, a reduction in the capacity of the dryer as required by the stresses the joint can withstand. Furthermore, if a bolted joint is used, as is fairly common in the art, this generally results in a thinner section at this point further complicating the problem. The bolt holes, corners and edges at the joint introduce stress raisers. Since this location is a location of maximum bending moment in the head, the fact that the stress raisers are located at this very point is particularly disadvantageous.

SUMMARY OF THE INVENTION In order to overcome the disadvantages pointed out above, a rotary pressure vessel, built in accordance with the teachings of this invention, comprises a head having an inner and outer portion. The inner portion of the head is integral with the journal and carries an attachment means in the shape of a circle around the outer edges of the inner head. An outer head, in the shape of an annulus is provided with first and second attachment means. The first attachment means is in the form of a circle at the inner edge of the annulus. The second attachment means is also in the shape of a circle at the outer edge of the annulus. The first attachment means is suitable for attaching the outer head to the inner head. In a like manner, the second attachment means attaches the head to the shell.

Furthermore, a right circular cylindrical brace is provided which can be attached to extend between a pair of outer heads. It is particularly advantageous to select the radius of the right cylindrical brace so that a standard flange may be employed in attaching the brace to the outer head. In addition, if properly selected in size, it may also be possible to employ standard size rolled pipe as another component in the brace.

Selection of the various radial dimensions of the inner and outer head is important to achieving the advantages of the present invention. In distinction to the joint at a location of maximum bending stress in the head, the present invention locates the joint attaching the inner and outer heads, at a point of low bending stress in the head. Particularly, the bending stress in the head varies with radial location and changes in sign from journal to shell. The joint between the inner and outer head is located at or near the inflection point of the stress in the head under normal operating conditions. This results in a low value of stress at the joint. The joint may advantageously be located in the vicinity of this point although not exactly at the point of inflection, if, such a location is compatible with the use of standard components.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are cross-sections of a journal, head and brace arrangements used in the prior art;

FIG. 3 is a cross-section of a journal, head and brace arrangement in accordance with the teachings of the present invention;

FIG. 4 is an end view of a rotary pressure vessel built in accordance with the present invention; and

FIG. 5 is a simplified illustration of the cross-section of FIG. 3 modified to show head distortion under operating conditions.

Detailed Description or heads 13, (only one of which is illustrated) close the ends of the shell to form a pressure containing vessel. The heads are mounted on a journal 16 for rotatable movement. The journal 16 is hollow forming conduit 22 to provide for the introduction ofa heat transfer medium, such as steam, into the interior of the dryer. In more detail, FIG. 1 illustrates that the head 13 comprises an outer head portion 13 in the shape of an annulus, and an inner head portion 13" which is formed integral with the journal 16. The outer head portion 13' has an attachment means 12 for attaching the outer head portion 13 to the shell 11. The attachment means 12 comprises bolt holes in both shell 11 and outer head 13' and bolts coupling shell 11 and outer head 13. Furthermore, the outer head portion 13 has another attachment means 17 for attaching the outer head portion to the inner head 13". The attachment means 17, likewise comprises bolt holes in both inner head 13" and outer head 13 and bolts connecting inner and outer heads. The journal 16 and inner head portion 13" are integrally formed. A brace 14 is provided, integral with the inner head portion 13. The brace takes the form of a right circular cylinder or inner shell.

The supporting structure for the journal comprises a tapered portion 18 on which a bearing 19 is mounted. The bearing 19 is supported by apparatus not shown. A locknut 20, threaded on a threaded portion of the journal 16, maintains the tapered portion 18 of the journal 16 in contact with the bearing 19.

As has been explained above the journal 16, inner head portion 13" and brace 14, being integral, comprise a substantially large component of the dryer. As a result, manufacture of this portion of the dryer is difficult for machining requires a very large boring mill or a lathe. The machining of the taper l8 and the threads for the locknut 20 are very difficult to accurately machine on such a boring mill.

FIG. 2 illustrates another variety of prior art dryer showing the shell-head-brace-journal elements. In particular a shell 41 is mounted to a pair of heads 23 (only a portion of one head 23 is shown). In turn the head 23 is attached to a flange 33 of a journal 26. Journal 26 is supported by apparatus not shown. The location of the attachment 37 is particularly disadvantageous, as has been explained above, by reason of the relatively larger stresses experienced as this location.

FIG. 3 illustrates the journal, head and head-shell interface of a rotary pressure vessel built in accordance with the present invention. In particular, the rotary pressure vessel may comprise a Yankee dryer. The journal 6, tapered portion 8, bearing 9, threads and locknut l0 and hollow shaft 12 are similar to the components 16, 18, 19, 20, and 22 illustrated in FIG. 1. Furthermore, similar to FIG. 1, the head 3 comprises an inner head portion 3", integral with the journal 6, and an outer head portion 3 in the shape of an annulus. Furthermore, the inner head portion 3 has an attachment means in the form of a series of bolt holes 7 at a radius R from the shaft in the outer edge thereof. The outer head portion 3', annular in form, carries an attachment means 7 comprising a circular series of bolt holes with said circle having a radius R. The attachment means 7 and 7' provide for a joint in the head. Furthermore, a second joint 2, joins the outer edge of the annulus 3 with the shell I. In addition, a right circular cylindrical brace 4 is illustrated. In particular, the brace 4 comprises a flange 14, which is joined to the head 3 at a joint 5, and a cylinder which maybe pipe or rolled plate is connected to the flange such as by weld I6. Since the cross-section illustratedin FIG.-2 is only the lower half of the entire head cross-section,-as is readily apparent to those skilled in the art, only one edge of brace 4 is illustrated.

One of the important features of this invention is the selection of the relative radial dimensions of the inner head portion 3" and outer head portion 3'. In particular. the radial location of the attachment means 7 is a significant portion of the present inventionj As is pointed out above some of the prior art dryer arrangements were disadvantageous by locating a joint in the vicinity of the journal. The reason that thi'sarrange ment is disadvantageous is that the stresses a'tth'at location are relatively high. It is desirable to minimize the stress on a joint for a number of reasons. The configuration of some typical joints include a number of stress concentration points which would subject the joint to rupture at stress levels which can easily be accommodated by an integral component. For this reason, for instance, the location of the joint 37 in FIG. 2 in the flange adjacent the journal is particularly disadvantageous. The stress that can be accommodated by the joint at this location is much less than the stress that can be accommodated in an integral journalhead, at this location. Analysis of the bending stresses, in the head, under actual operating conditions, shows that the bending moment changes direction as a function of radial distance. Therefore, I choose to locate my joint 7 at a location at or adjacent the inflection point of the bending stresses of the head. By reason of this selection, the bending stresses exerted at the joint 7 are relatively low. However, it is not necessary to locate the joint 7 directly at the inflection point since other advantages may flow from moving the joint slightly off the inflection point. For example, using the finite element method which represents the most advanced computer stress calculation method now in common use, the point of stress inflection in the head of a dryer of 18 foot diameter, is at a radius of thirty inches from the axis. Therefore, locating the joint 7 at a radius of inches would satisfy the criteria of this invention. However, other considerations may make it desirable to vary the location of the joint. For example, when building a dryer in accordance with this invention, a drill jig of 65 inch diameter may be available for drilling the bolt holes. By utilizing such drill jigs the actual joint 7 would be 2% inches from the inflection point. Considering the fact that this drill jig could be available, it would be advantageous to use it to drill the bolt holes and to locate the joint at 32% inches from the axis. This small deviation from the inflection point would be acceptable.

Referring nbw to FIG. 5, this illustrates a crosssection similar to that illustrated in FIG. 2, with the journal detail and joint 7 details omitted. The dotted showings in FIG. 4 illustrate the shape assumed by the head 3 under actual operating conditions. Dash line 13 illustrates the inflection point in the inner head portion 3". It is at this point that the theoretically ideal joint 7 would be located in accordance with the principles of my invention. The deformation illustrated in FIG. 4 is caused by the influence of heat, pressure and other operating parameters and has been exaggerated for purposes of illustration.

One particular advantage of locating the joint 7 at or adjacent the inflection point is that while the head enjoys the advantages of an integral head-journal combination, the structure is not so large as to make machiningdifficult. Thus, for instance, the journal-inner head portion 3'l can easily be machined on-a small boring mill orlathe.

-Referringagain to FIG. 3, the brace 4 comprises a flange 14 joined to a cylinder 15 which may be formed of pipe or rolled plate l5'such as by welding at the location 16. As is well known to those skilled in the art, the brace 4 extends from one head to a parallel head and, in accordance withmy invention, the brace 4 extends between two outer head portions 3'. The location of the brace 4 on the head depends upon a number of side diameter of the brace cylinder is 102% inches and the diamter of the joint 5 is 108 /2 inches. For smaller dryers, it may be possible to reduce costs even further by making the cylinder 15 of such a diameter that it may be formed from standard pipe.

From the foregoing it will be apparent that the dryer head disclosed herein enjoys a number of the advantageous features of the prior art while, at the same time eliminating the disadvantageous features which the prior art introduced. In particular, the joint 7 is located at or adjacent to the inflection point of the head under actual operating conditions so as to minimize the stresses to which the joint 7 is subjected. Furthermore, the brace 4 is sized and connected to the head 3 in such a manner that it plays the necessary supporting role but 'may comprise cheaper standard sized components rather than specially produced, and therefore more expensive ones.

Although the foregoing description includes a reference to bolted joints, those skilled in the art will under stand that other attachment means could be used in place of bolts. For example, welds and the like could be used in place of some or all of the bolted joints.

What I claim is:

1. In a rotary pressure vessel mounted on a journal with a shell, of the type used to dry slurries and webs, a multi-component head comprising,

an inner head integral with said journal and having an outer edge including attachment means of circular shape with a radius R, an outer head of annular shape with first and second attachment means on inner and outer edges thereof, respectively, said first attachment means of circular shape with a radius R, said first attachment means connected to said inner head attachment means and said second attachment means connected to said shell, said radius R selected at or adjacent a point of inflection of bending stress in said head.

5 2. The apparatus of claim 1 which comprises a third 3. A rotary pressure vessel mounted for rotation on a shaft, of the type used to dry slurries and webs, comprising,

a shell a pair of journals, each mounted onsaid shaft at opditions.

4. The rotary pressure vessel of claim 3 which further includes brace means connected between said pair of said second partial heads.

5. The apparatus of claim 4 in which said brace means comprises a right circular cylinder.

6. The apparatus of claim 5 in which said brace means also includes a pair of flanges, each connected to one'end of said circular cylinder, each of said flanges connected to one of said pair of second partial heads.

7. The apparatus of claim 6 in which each said flange is a standard size.

8. The apparatus of claim 7 in which each of said flanges are welded to said right circular cylinder. 

1. In a rotary pressure vessel mounted on a journal with a shell, of the type used to dry slurries and webs, a multicomponent head comprising, an inner head integral with said journal and having an outer edge including attachment means of circular shape with a radius R, an outer head of annular shape with first and second attachment means on inner and outer edges thereof, respectively, said first attachment means of circular shape with a radius R, said first attachment means connected to said inner head attachment means and said second attachment means connected to said shell, said radius R selected at or adjacent a point of inflection of bending stress in said head.
 2. The apparatus of claim 1 which comprises a third attachment means located on said outer head, intermediate said first and second attachment means, adapted to be connected to a brace for said head.
 3. A rotary pressure vessel mounted for rotation on a shaft, of the type used to dry slurries and webs, comprising, a shell a pair of journals, each mounted on said shaft at opposite ends of said shell, and each forming a partial head for said vessel, each said partial head extending substantially perpendicular to said shaft with an attachment means at an outer edge thereof in the shape of a circle, at a radius R from said shaft, a pair of second partial heads, each of annular form with inner radius R, extending substantially perpendicular to said shaft and each connected between said partial head and said shell, said radius R selected at or adjacent a point of stress inflection in said head under actual operating conditions.
 4. The rotary pressure vessel of claim 3 which further includes brace means connected between said pair of said second partial heads.
 5. The apparatus of claim 4 in which said brace means comprises a right circular cylinder.
 6. The apparatus of claim 5 in which said brace means also includes a pair of flanges, each connected to one end of said circular cylinder, each of said flanges connected to one of said pair of second partial heads.
 7. The apparatus of claim 6 in which each said flange is a standard size.
 8. The apparatus of claim 7 in which each of said flanges are welded to said right circular cylinder. 